The concept of indicating wetness in an absorbent article, especially a diaper, by a wetness indicator, which by a colour change indicates the presence of body fluid in the diaper, is previously known.
Thus a wetness indicating diaper is known through U.S. Pat. No. 5,197,958 provided by printing a pattern by a thermochromic ink on the exterior surface of the outer coversheet of a diaper. This pattern of thermochromic ink becomes visible or changes colour when a selected temperature is exceeded, adapted to indicate that the diaper has been wetted by body fluid.
EP-A-0 347 657 discloses a wetness indicating hot-melt adhesive which changes colour in response to the presence of moisture. The hot-melt adhesive contains particles of a dyestuff which is insoluble in the adhesive composition, but which are soluble in water. The hot-melt adhesive can be used in a diaper as a wetness indicator.
U.S. Pat. No. 5,167,652 discloses a moisture sensitive film produced by blending a copolyester with a moisture absorbing copolyamide. The film turns white when wetted. The film may be used as a diaper backsheet to indicate when the diaper has been wetted.
There is however a continuing need for improvement and for more sophisticated ways of indicating an increase or decrease in temperature in an absorbent article above a selected threshold value, for example in order to indicate the presence of body fluid, to indicate fever of the wearer or for visual and to enhance the customer product perception. Alternatively it may be desired to make a welding pattern more visible by means of a differing colour.